What Is Testosterone? A Complete Guide

Written by
Alastair Kennett
Medically approved by

Dr Chris Airey

Last updated
11th February 2024

Although testosterone is one of the most essential hormones in the body for males, many of us aren’t aware of its vital role in developing and maintaining the male body. Testosterone can help regulate many things we take for granted, such as memory, concentration, sex drive, and hair growth.

If you want to know more about how testosterone affects your daily life, the signs and symptoms of testosterone deficiency, or how to diagnose and treat low testosterone levels, keep reading to find out everything you need to know in this comprehensive guide.

testosterone what is

What is Testosterone?

Testosterone is a hormone mainly produced in the testes or ovaries, but your adrenal glands can also make it. Testosterone is also an androgen, which means it’s responsible for developing male characteristics, such as body hair and a deeper voice. It also helps to develop the penis and testes, is responsible for sperm production, and can increase muscle strength and size.

People born as a male have the highest testosterone levels and these hormone spikes during puberty. If you have too much or too little of the hormone, you can experience various health issues.

Testosterone Production and Regulation

Testosterone is first produced during foetal development, which is how testicles and other male characteristics develop. Testosterone then spikes during puberty and is responsible for a change in males, such as the enlargement of the testes and penis, an increase in sex drive, and an increase in height.

In adult males, testosterone produces sperm and red blood cells, improves bone and muscle mass, and can regulate sexual function and mood. Testosterone is also found in females and enhances sex drive. Testosterone in females is converted into oestradiol, which is used to mature and maintain the female reproductive system.

From age 30, testosterone production decreases by around 1 to 2% each year.

Your testosterone levels are at their highest point when you wake up in the morning and decrease throughout the day. The pituitary gland and hypothalamus (located in your brain) regulate when testosterone is released. They do this with the help of several hormones.

In healthy testosterone production, the hypothalamus releases gonadotrophin-releasing hormone (GnRH). This hormone signals to your pituitary gland to release a second hormone called luteinising hormone (LH). LH travels through your bloodstream to your testes, which triggers the production and release of testosterone.

As your testosterone levels increase, this stops or lessens the amount of GnRH produced and released. This is how your body regulates and maintains normal testosterone levels.

Certain health conditions can cause hormonal imbalances and issues with your hypothalamus or pituitary gland, making it harder to regulate your hormones. A hormone imbalance can also be caused or worsened by certain lifestyle factors, such as diet.

Normal Testosterone Levels by Age

If you are born as a male, your testosterone levels by age are as follows:

●        0 to 5 years: less than 12 ng/dL (nanograms per decilitre)

●        6 to 10 years: less than 25 ng/dL

●        11 to 15 years: less than 830 ng/dL

●        16 to 17 years: 102 to 1010 ng/dL

●        18 to 99 years: 193 to 824 ng/dL

If you are born as a female, your testosterone levels by age are as follows:

●        Under 1 year: less than 21 ng/dL

●        1 to 5 years: less than 12 ng/dL

●        6 to 10 years: less than 25 ng/dL

●        11 to 17 years: less than 79 ng/dL

●        18 to 99 years: less than 40 ng/dL

Signs and Symptoms of Low Testosterone

The signs and symptoms of testosterone deficiency usually only affect males who were assigned that gender at birth. In medical terms, low testosterone is called male hypogonadism. You can either have congenital or acquired hypogonadism.

Congenital hypogonadism means you have low testosterone from birth, perhaps because of a genetic defect or medical condition. Acquired means having low testosterone levels in later life, perhaps because of a medical condition or a condition affecting the normal functioning of any organ associated with testosterone regulation and production.

If you have testosterone deficiency during puberty, the signs and symptoms include:

●        Reduced development of pubic and body hair

●        Delayed height growth, but arms and legs may still grow and become unproportionate with the rest of the body

●        Little or no change in voice

●        Little or no development of the testes and penis

●        Reduced strength, muscle mass, and endurance

In adult males, the signs and symptoms of testosterone deficiency can include:

●        Loss of body and pubic hair

●        Low mood, depression, stress, or anxiety

●        Osteoporosis, a condition where bones are weakened and are more likely to fracture or break

●        Low sex drive

●        Erectile dysfunction

●        An unexplained increase in body fat and reduction in muscle mass and strength, despite no changes to your diet and exercise regime

●        Difficulty falling or staying asleep

●        Difficulty with memory or concentration

●        A decrease in sperm reduction, which will show up on fertility tests

man low testosterone sign

Diagnosis of Low Testosterone

A blood test is the only way to diagnose low testosterone. You can do this through a private clinic, an online pharmacy, or GP. If you visit a doctor, they will discuss your symptoms before booking you in for a TRT blood test that will check testosterone levels and other hormones in your blood responsible for testosterone production and regulation.

You can also do a testosterone home test kit, which involves taking a blood sample through a finger prick test. This should be in the morning when testosterone levels are at their highest. You may need more than one blood test to confirm low testosterone.

A doctor may perform other tests alongside a blood test to rule out conditions like infection. If your testosterone levels are below normal for your age, you will be diagnosed with hypogonadism. You will either be prescribed TRT (testosterone replacement therapy) or referred to a specialist known as an endocrinologist, who can prescribe TRT.

Treatment Options for Low Testosterone

If you have low testosterone, you can be prescribed testosterone replacement therapy. This can help your body to maintain a normal testosterone level and treat any symptoms associated with low testosterone.

There are many ways to administer TRT, such as an injection, gel, or patch. You can get TRT prescribed by a doctor or online pharmacy, but you should only use TRT if you have a clinical diagnosis of low testosterone.

treatment low testosterone

You may also be treated for the cause of the condition, depending on what is causing low testosterone in the first place. For example, if lifestyle factors are affecting your ability to produce testosterone, your doctor may suggest:

●        Changing your diet to a healthy balanced diet full of foods that can help boost testosterone, such as shellfish and leafy green vegetables

●        Losing weight (if you are overweight or obese on the BMI (body mass index) scale)

●        Quitting smoking

●        Limiting your alcohol intake

●        Doing exercise that increases testosterone and improves muscle mass, especially weight training

Another treatment option for low testosterone is natural testosterone boosters. These are supplements that are 100% safe and legal. Bear in mind that we are not talking about any kind of steroid boosters you can get on the black market, but testosterone boosters made with natural ingredients that are regulated for your safety.

In most men, these natural ingredients can help boost testosterone levels and hormone production, positively affecting testosterone regulation.

Risks and Side Effects of Testosterone Therapy

Like any medication, testosterone therapy has some risks, so you should only use it under a doctor’s care. Your doctor can make sure TRT is suitable for you before prescribing it and may do some tests to ensure that TRT won’t cause more harm than good.

It can also negatively affect you if you take TRT when you don’t need it, or your testosterone levels become too high. The risks and side effects of testosterone therapy include:

●        Acne or other skin reactions.

●        A worsening of sleep apnoea – potentially serious condition that affects your breathing during sleep.

●        Enlargement of breast tissue.

●        Stimulation of noncancerous growth of the prostate, known as benign prostatic hyperplasia. Whilst not cancerous, this can cause pain and difficulty urinating.

●        Development of existing prostate cancer. You should not take TRT or testosterone boosters if you have been diagnosed with prostate cancer and are currently receiving treatment.

●        Shrinking of testicles.

●        Limited sperm reduction.

●        Overstimulation of red blood cell production, which can cause an increased risk of blood clots.

If you cannot take TRT or get unwanted side effects, speak to your doctor about other testosterone treatment options. Lifestyle changes can improve testosterone levels with the help of natural testosterone boosters, or you may be able to treat the cause of the problem.


Testosterone is an important hormone that regulates mood, sexual function, healthy blood cell production, muscle mass, and weight. Testosterone deficiency is also known as hypogonadism. Symptoms can include low sex drive, an increase in body weight, erectile dysfunction, a decrease in muscle mass, and loss of body hair.

Testosterone levels will slowly decrease with age, but this shouldn’t cause any issues. If you believe your testosterone levels are lower than average, you should get a blood test. If you are diagnosed with low testosterone, you can be prescribed testosterone replacement therapy, incorporate natural ways to boost testosterone into your lifestyle, or try natural testosterone boosters.

While we've ensured that everything you read on the Health Centre is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. It should never be relied upon for specific medical advice. If you have any questions or concerns, please talk to your doctor.

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